Tweezer Cleaning Process Generates Lots of Particles

Ed Myers edmyers at
Mon Nov 5 14:40:28 PST 2007

Whoops, here is the CTFE resistance.

At 02:35 PM 11/5/2007, Ed Myers wrote:
>I've looked over a number of web sites related to chemical 
>resistance of plastics.  Jim is right, Delrin does not fit with our 
>cleaning procedure.  It has low chemical resistance to most acids, 
>but is fine with our solvents.  Looking for an alternative, the 
>leading candidates come from the fluorocarbon plastics such as 
>CTFE.  It so happens we stock a CTFE tweezers.
>567 Fluorocarbon (CTFE) for use in Chemical Processing of 
>semiconductors. Withstands Hydrofluoric and other acid,.
>Resists radiation. 6-3/8"x15/32" body
>tapering down to .009" by 3/32" at Tweezer Tips Extra long with 
>line-up pin guide.
>We should review the cost of these tweezers and decide if we want to 
>stock CTFE exclusively or make not of appropriate cleans and 
>applications for the different wafer types.  At the very least we 
>need to stop the mentioned cleaning procedure on the Delrin version.
>At 02:50 PM 9/10/2007, Jim McVittie wrote:
>>I have a problem with our recommended cleaning procedure for Delrin
>>tweezers.  It attacks the Delrin surface and causes the tweezers to leave
>>particles on the wafers.  Today, I was helping a student do a TEL plasma
>>oxidation. When he loaded his wafer, we spotted particles. We traced the
>>particles to his Delrin tweezers. On quizzing him, I found that he had
>>followed the cleaning procedure on our website.
>>Here is the procedure in question:
>>Delrin (plastic) Tweezers:
>>1. Remove trace metals for 5 min in unheated 5:1:1 H2O:H2O2:HCl.
>>2. Rinse for 4 min in DI water.
>>3. Remove organics for 5 min in unheated 5:1:1 H2O:H2O2 :NH4OH
>>4. Rinse for 4 min in DI water.
>>5. Blow dry using N2 gun at the wetbench.
>>6. Place tweezers in a clean storage box with the tips oriented toward the
>>end of the box marked TIPS. This will insure that comtaminates from gloved
>>hands and fingers will not transfer to the ends of the tweezers which will
>>be in contact with the wafers.
>>There are a number of problems with this clean. For one a standard clean
>>should always start with an organic clean step to expose the metal
>>contamination so the following HCl step can remove the metal. Another
>>problem is that it dose not address the issue that Delrin is an organic
>>and is attacked by the H2O2 and most acids. Although it can stand up to
>>bases, such as NaOH and KOH, it does not hold up well to NH4OH.
>>Since Delvin is compatible with most solvents, I suggest we limit our
>>Delrin cleaning to solvent rinses. In addition, I suggest we look for
>>plastic tweezers which are compatible with some of our standard acid, such
>>as HF and HCl.
>>The chemical compatibility of Delvin can be found at:
>>         Jim
>>Jim McVittie, Ph.D.                     Senior Research Scientist
>>Allen Center for Integrated Systems     Electrical Engineering
>>Stanford University                     jmcvittie at
>>Rm. 336, 330 Serra Mall                 Fax: (650) 723-4659
>>Stanford, CA 94305-4075                 Tel: (650) 725-3640
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